In recent years, liquid discharge apparatuses adapted for discharging ink droplet from an ink discharge unit to carry out recording with respect to recording paper, e.g., ink jet printers have been popularized. In such ink jet printers, ink jet printers of the type which discharge ink droplet while moving, in a direction perpendicular to paper feed direction, recording head in which ink discharge units are arranged at several millimeter width in paper feed direction are widely popularized. Hereinafter, such recording head will be called serial head.
In ink jet printers of such serial head type, it is necessary to print one image by several scanning operations. As a result, it takes much time for completing printing. Such printers have the problems that the number of scanning operations of the head is many so that burden is applied to the apparatus, and occurrence frequency of noise is increased, etc.
In view of the above, it is conceivable to use ink jet printer in which plural ink discharge units are arranged in a direction perpendicular to paper feed direction, e.g., ink jet printer of the type in which a large number of ink discharge units are arranged within the range equivalent to print range in a direction perpendicular to the paper feed direction, or within a range broader than that range to print image by one paper feed, i.e., one scanning operation in head relative movement direction. Hereinafter, head of the type in which a large number of ink discharge units are arranged in a direction perpendicular to the paper feed direction, and recording paper is relatively moved in one direction with respect to the recording head will be called line head. In the line head, there are the type in which recording head is fixed and recording paper is moved, and the type in which recording paper is fixed and recording head is moved.
Meanwhile, picture quality required for the ink jet printer has been improved year by year, and realization of high resolution has been advanced. In accordance with such circumstances, size of ink droplet to be discharged also has become small.
In accordance with realization of high resolution of image to be printed and change into very small ink liquid droplet, realization of high accuracy is required also with respect to impact position of ink droplet, i.e., formation position of dots on recording paper. In the ink jet printer, there are instances where impact position of ink droplet may deviate (be shifted) from the primary position by influence such as accuracy of ink discharge unit and/or state of nozzle surface constituting the ink discharge unit, etc. With respect to such positional shift, there are some positional shifts taking place at random every time, but positional shift resulting from accuracy of the ink discharge unit, etc. is peculiar to respective discharge units.
Accordingly, when image is printed by one scanning operation by means of line head, tendency of positional shift peculiar to respective ink discharge units is maintained from the first to the last. For this reason, particularly when impact position is shifted to the ink discharge unit arrangement direction, stripes take place along print direction as shown in FIG. 17 which will be described later.
In the case where dot diameter is sufficiently small as compared to resolution, such stripes are difficult to be conspicuous because the portion of white ground is many. However, in the case of dot diameter equivalent to pitch of pixel or slightly greater than that, such stripes are divided into the portions of white stripe and the portions which are not the white stripe so that they become conspicuous.
In this case, there are also instances where inks are pulled against each other so that shift of impact position is further enlarged as shown in FIG. 18 which will be described later independency upon property of ink and paper.
This problem similarly takes place even in the case of the serial head without being limited to the line head. In this case, in the serial head, with respect to this problem, without printing print direction same line only by one ink discharge unit, paper feed quantity is controlled to print the same line in the print direction by using plural different ink discharge units, or to carry out print by one scanning operation thereafter to carry out scanning operations several times in such a manner to fill space of print result to carry out print so that such stripes are caused to be difficult to be conspicuous.
In this method, there were drawbacks that because the number of scanning operations of head required for print is increased, it takes much time, burden is applied to the apparatus, occurrence frequency of noise is further increased, and data for driving head must be complicatedly sorted, etc.
In the case of the line head, the greatest merit that print can be made by one scanning operation would not be exhibited.